1. Field of the Invention
The present invention relates to a wheel support apparatus for a carriage capable of not only a back-and-forth run but also complicated runs such as a spin turn, a traverse run, and an oblique run. More particularly, the invention relates to a wheel support apparatus for a carriage including a pair of wheels spaced apart in a direction of an axis of rotation, motors for driving the wheels individually, and a wheel support frame supporting the wheels and motors and connected to a body frame through a bearing to be pivotable about a vertical axis defined in a middle position between the wheels.
2. Description of the Related Art
FIG. 20 shows an example of conventional wheel support apparatus using a bearing 63 as proposed in Japanese Utility Model Publications "Kokai" No. 61-13102 and No. 2-103879, for example.
More particularly, a wheel support frame 62 supports a pair of wheels 31A and 31B spaced apart from each other in a direction of an axis of rotation and motors 33A and 33B for driving the wheels 31A and 31B, respectively. The wheel support frame 62 is pivotable about a vertical axis P located in an intermediate position between the wheels 31A and 31B. A drive wheel assembly 3' of a carriage having the wheel support frame 62 is attached to a body frame 2' by a rotary shaft frame 62a fixed to an upper portion of the wheel support frame 62 through a bearing 63 and a frame 61.
Thus, the motors 33A and 33B are rotated independently to vary a direction of the drive wheel assembly 3' about the vertical axis P.
Numeral 32 denotes axles of the wheels 31A and 31B, and numeral 62b denotes a frame suspended from the frame 62 for supporting a middle position between the axles 32. Numerals 63a and 63b denote an inner race and an outer race of the bearing 63, respectively.
According to the conventional apparatus, however, it is absolutely necessary to secure a space between upper edges of the wheels 31A and 31B and the body frame 2' for accommodating the wheel support mechanism including the rotary shaft frame 62a, the bearing 63 and the frame 61. The body frame 2' is not permitted to be lower toward the wheels than the illustrated height. As a result, a compact vehicle is not provided.